Pros

Cons

✕Virtualised data layers can be complex to configure and manage

✕some applications can’t be virtualised

✕may be identified as a rootkit by some security programs

If there was ever an application designed to 'blow your socks off', it has to be the Software Virtualisation Solution (SVS) from Altiris. Why? Because it lets you install complete Windows applications in seconds, run them without affecting anything else on the host PC, and remove them again just as quickly and easily. Imagine it: using SVS you can check out new application releases without being forced to upgrade the existing version; test beta code without fear of corrupting other programs or data files; reset applications to their just-installed state at the click of a mouse button; and a whole lot more besides.

The concepts involved take a little understanding, but they’re not that difficult. Unlike virtualisation tools from companies such as VMWare and Microsoft, the Altiris software doesn’t attempt to virtualise the complete PC, just the application environment. It does this by installing a small agent that fools the host operating system into thinking it’s running a normal application, when in fact all the associated file and registry calls are redirected to what Altiris calls a virtual 'layer', where the application actually resides.

Several applications can installed together into the same layer or they can be configured separately in their own individual environments, avoiding any potential conflicts entirely. The initial layer created when the application is installed is also read-only, so it can’t be corrupted; an associated but separate read/write layer is used to hold the program data, configuration files and so on. Delete that and -- voila -- the application is returned immediately to its just-installed condition.

There are two ways to install a virtual application. The first is to create a new layer using the optional Admin console, whereupon you’ll be promoted to browse for and run the setup program for the application concerned. Any file and registry changes are then captured and stored in a special folder, creating a virtual software package (VSP) rather than installing the application directly.

The other way is to import an existing VSP. This can be one you’ve created and then exported yourself, or a prebuilt package from a third party. Altiris, for example, has a number of ready-to-use open source virtual applications that can be downloaded from its support site, Juice.

Once the virtual application is installed, you simply activate it to make it available to the host Windows OS. You also have the option of activating automatically each time Windows starts. Hit the activate button and the normal desktop icons, Start menu entries and so on appear, ready to use. Deactivate and it’s as though the application never existed.

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For the most part, SVS is easy to use and quick. For example, having downloaded and installed the agent onto a Windows XP PC (a process that took about a minute), it took only a few more minutes to create a new layer and install a full copy of OpenOffice.org 2.0. We were then able to archive and distribute this VSP, installing it on other Windows XP and Windows 2000 PCs running the agent almost instantly.

Performance doesn’t appear to be affected either. Altiris reckons on a 2-3 percent processing overhead, but we didn’t notice and we really liked what we saw. In fact we liked it a lot, and would have given Altiris SVS 2.0 an unprecedented Editors' rating of 10 if it hadn’t been for a couple of concerns during testing.

The biggest concern is the way that documents and files created or updated by a virtual application are redirected to its read/write layer. This is not a problem as long as the layer is activated; but if it’s de-activated for any reason, those files disappear -- instantly prompting a call to the help desk if you don’t know what’s going on. Moreover, if an application needs to be reset (because it gets corrupted, for instance), the read/write layer is deleted along with any files it may contain.

To get around this you need either to make sure that users save their work to a network drive (as those resources aren’t redirected) or set up one or more virtual data layers.

Data layers are standalone virtual layers that can be activated and used independently of virtualised applications. They can be associated with particular local folders or file types so that any new files or updates will be automatically redirected to the virtual world. You can also 'seed' and manage data layers by moving files back and forth between real and virtual storage areas.

All of this works, and it makes for portability of data as well as applications. However, it takes a while to get your head around the concepts involved, and management could be a real headache -- especially where lots of relatively non-technical users are involved.

There can also be problems with applications that bypass the APIs used by the SVS agent to intercept file and registry access. Applications such as antivirus scanners, for example, may not work if virtualised using SVS. Neither can it be used to virtualise server applications or device drivers. Plus some anti-spyware utilities report the agent as suspect, even identifying it as a potential rootkit.

And, of course, care is needed in terms of application licensing: SVS provides the potential to drive a coach and horses through carefully crafted enforcement policies if it's not managed properly.

Still, such gripes aside, Altiris Software Virtualisation Solution is a great tool. It may not be for everyone, but developers, application testers and other power users who need to run applications that would otherwise conflict and interfere with each other will find it invaluable. Best of all, you can download and use SVS for free (although commercial deployments cost £18.90 ex. VAT per client): our betting is that you’ll soon wonder how you managed without it.

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